The proposed research will continue our work in the area of the regulation of fuel metabolism. Lipid energy is transported in the blood in several forms, including chylomicrons and free fatty acids (FFA). Chylomicrons are key elements in the absorption and storage of dietary fat, and also play a role in the pathogenesis of atherosclerosis via the production of remnant particles. FFA are the major lipid fuel in the body, and increases in their concentration have been shown to cause insulin resistance, endothelial dysfunction, increases in the production of very low density lipoproteins, and increases in blood pressure. FFA are released into the blood through the action of hormone sensitive lipase on triglyceride stores in fat cells. Very little is known about the role of chylomicrons in FFA metabolism, but available evidence suggests that chylomicrons are also a major source of FFA. Extremely accurate and precise methods have been developed by the investigator for the measurement of the concentration and specific activity of FFA and chylomicron triglyceride fatty acids in plasma. In addition, a tracer method for accurately determining the kinetics of chylomicrons has been developed. Preliminary results indicate that approximately 40% of chylomicron fatty acids are released into the circulation as FFA during their metabolism by lipoprotein lipase, and that this release may be greater in adipose tissue than in skeletal muscle. In the proposed studies, the tracer technique will be used to systematically investigate the contribution of chylomicrons to total FFA availability. The technique will be applied to normal subjects at rest and after exercise, as well as subjects with type 2 diabetes mellitus and hypertriglyceridemia. Specifically, these studies will 1) determine the relative contribution of chylomicrons in adipose tissue versus muscle to FFA production and further validate the isotopic method for quantifying chylomicron triglyceride kinetics; 2) determine the relationship between meal fat content and the production of FFA from chylomicrons; 3) characterize FFA production from chylomicrons in subjects with type 2 diabetes and the effect of acute insulin therapy on that process; and 4) determine whether exercise sufficient to lower the chylomicronemic response to a meal results in increased efficiency of regional and systemic chylomicron fatty acid uptake in normal subjects. These studies will provide new insights into the regulation of FFA metabolism in humans.